man/man3ofmt/ofmt.3ofmt

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.\" Copyright 2018 Joyent, Inc.
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.Dd December 20, 2018
.Dt OFMT 3OFMT
.Os
.Sh NAME
.Nm ofmt_open ,
.Nm ofmt_print ,
.Nm ofmt_update_winsize ,
.Nm ofmt_strerror ,
.Nm ofmt_close
.Nd data structures and routines for printing output
.Sh LIBRARY
.Lb libofmt
.Sh SYNOPSIS
.In ofmt.h
.Ft ofmt_status_t
.Fo ofmt_open
.Fa "const char *fields"
.Fa "const ofmt_field_t *template"
.Fa "uint_t flags"
.Fa "uint_t maxcols"
.Fa "ofmt_handle_t *ofmt"
.Fc
.Ft void
.Fo ofmt_print
.Fa "ofmt_handle_t ofmt"
.Fa "void *cbarg"
.Fc
.Ft void
.Fo ofmt_update_winsize
.Fa "ofmt_handle_t ofmt"
.Fc
.Ft "char *"
.Fo ofmt_strerror
.Fa "ofmt_handle_t ofmt"
.Fa "ofmt_status_t error"
.Fa "char *buf"
.Fa "uint_t bufsize"
.Fc
.Ft void
.Fo ofmt_close
.Fa "ofmt_handle_t ofmt"
.Fc
.Sh DESCRIPTION
The
.Nm libofmt
library provides data structures and routines for printing output.
.Pp
Currently this is an internal interface.
The interface can and will change without notice as the project needs, at any
time.
.Pp
All output is assumed to be in a columnar format, where each column represents
a field to be printed out.
Multiple fields in parsable output are separated by
.Sq \&: ,
with the
.Sq \&:
character itself escaped by a
.Sq \e
.Po e.g., IPv6 addresses  may be printed as
.Qq fe80\e:\e:1
.Pc ;
single field output is printed as-is.
In multiline mode, every
.Bq field,value
pair is printed in a line of its own, thus:
.Qq field: value .
.Ss Data Structures
The
.Vt ofmt_field_t
data structure used in
.Sx ofmt_open
is defined as follows:
.Bd -literal
typedef struct ofmt_field_s {
	char	*of_name;	/* column name */
	uint_t	of_width;	/* output column width */
	uint_t	of_id;		/* implementation specific cookie */
	ofmt_cb_t *of_cb;	/* callback function defined by caller */
} ofmt_field_t;
.Ed
.Pp
The
.Vt ofmt_arg_t
data structure which is passed to callback function is defined as follows:
.Bd -literal
typedef struct ofmt_arg_s {
	uint_t	ofmt_id;	/* implementation specific cookie */
	uint_t	ofmt_width;	/* output column width */
	uint_t	ofmt_index;	/* unused */
	void	*ofmt_cbarg;	/* argument passed to ofmt_print() */
} ofmt_arg_t;
.Ed
.Ss Fn ofmt_open
The
.Fn ofmt_open
function opens a handle returned in
.Fa ofmt
for each set of fields to be printed.
.Pp
.Fa fields
is a comma-separated list of the fields that have been selected for output
.Po typically the string passed to
.Fl o
in the command-line
.Pc .
Columns selected for output are identified by a match between the
.Va of_name
value in the
.Fa template
and the
.Fa fields
requested.
In human-friendly
.Pq non machine-parsable
mode,
.Dv NULL
.Fa fields ,
or a value of
.Qq all
is treated as a request to print all allowable fields that fit other applicable
constraints.
.Pp
.Fa template
specifies the list of supported fields, along with formatting information
.Pq e.g., field width ,
and a pointer to a callback function that can provide a string representation of
the value to be printed out.
The set of supported fields must be a
.Dv NULL
terminated array of type
.Vt ofmt_field_t ,
described in
.Sx Data Structures ,
as follows:
.Bd -literal -offset indent
{<of_name>, <of_width>, <of_id>, <of_cb> },
\&.\&.\&.
{<of_name>, <of_width>, <of_id>, <of_cb> },
{NULL, 0, 0, NULL}
.Ed
.Pp
.Va of_cb
is the application-specified callback function with the following prototype that
provides a string representation of the value to be printed for the field:
.Bd -literal -offset indent
boolean_t (*of_cb)(ofmt_arg_t *ofmt_arg, char *buf, uint_t bufsize)
.Ed
.Pp
The callback must not write beyond
.Fa bufsize
bytes of the string form into
.Fa buf .
If the function successfully translates the field into its string
representation and places it into
.Fa buf ,
then the callback function should return
.Dv B_TRUE .
Otherwise, the callback function should return
.Dv B_FALSE .
.Pp
The interpretation of the
.Va of_id
field is completely private to the caller, and can be optionally used by the
callback function as a cookie to identify the field being printed when a single
callback function is shared between multiple
.Fa template
entries.
.Pp
The
.Fa flags
can be any valid combination of the following:
.Pp
.Bl -tag -width "OFMT_MULTILINE" -compact
.It Dv OFMT_PARSABLE
Machine-parsable mode.
Specifying a null or empty
.Va fields
in the machine-parsable mode will result in a returned error value of
.Dv OFMT_EPARSENONE .
An attempt to create a handle in machine-parsable mode with the
.Fa fields
set to
.Qq all
will result in a returned error value of
.Dv OFMT_EPARSEALL .
.It Dv OFMT_WRAP
Wrap output if field width is exceeded.
Currently output is wrapped at whitespace or comma characters.
.It Dv OFMT_MULTILINE
Multiline mode.
Specifying both
.Dv OFMT_MULTILINE
and
.Dv OFMT_PARSABLE
will result in
.Dv OFMT_EPARSEMULTI .
.It Dv OFMT_RIGHTJUST
Right justified output.
.El
.Pp
The non-zero
.Fa maxcols
limits the number of output columns.
.Ss Fn ofmt_print
The
.Fn ofmt_print
function prints a row of output.
.Pp
.Fa cbarg
points at the arguments to be passed to the callback function for each column in
the row.
The call to
.Fn ofmt_print
will result in the callback function of each selected field invoked with
.Va of_id ,
.Va of_width
and
.Fa cbarg
embedded in
.Fa ofmt_arg ,
described in
.Sx Data Structures .
.Pp
The callback function should fill
.Fa buf
with the string to be printed for the field using the data in
.Fa cbarg .
.Ss Fn ofmt_update_winsize
The
.Fn ofmt_update_winsize
function updates the window size information
.Pq which is initially computed when the handle is created
in the
.Fa ofmt .
If the
.Dv TIOCGWINSZ
ioctl fails, the window size is set to 80x24.
.Ss Fn ofmt_strerror
The
.Fn ofmt_strerror
function returns error diagnostics in
.Fa buf
using the information in the
.Fa ofmt
and
.Fa error .
.Pp
Using a
.Fa buf
size of
.Dv OFMT_BUFSIZE
is recommended.
.Ss Fn ofmt_close
The
.Fn ofmt_close
function frees any resources allocated for the handle after printing is
completed.
.Sh RETURN VALUES
If successful, the
.Fn ofmt_open
function will return
.Dv OFMT_SUCCESS ,
with a non-null
.Fa ofmt_handle .
The function returns one of the failure codes
.Po enumerated in
.Vt ofmt_status_t
.Pc
listed below otherwise:
.Pp
.Bl -tag -width "OFMT_ENOTEMPLATE" -compact
.It Dv OFMT_ENOMEM
out of memory
.It Dv OFMT_EBADFIELDS
one or more bad fields with good fields
.It Dv OFMT_ENOFIELDS
no valid output fields
.It Dv OFMT_EPARSEALL
"all" is invalid in parsable mode
.It Dv OFMT_EPARSENONE
output fields missing in parsable mode
.It Dv OFMT_EPARSEWRAP
parsable mode incompatible with wrap mode
.It Dv OFMT_ENOTEMPLATE
no template provided for fields
.It Dv OFMT_EPARSEMULTI
parsable and multiline don't mix
.El
.Pp
More information about the type of failure can be obtained by calling
.Fn ofmt_strerror .
.Pp
The
.Fn ofmt_strerror
function returns the
.Fa buf .
.Sh INTERFACE STABILITY
.Sy Private .
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr strerror 3C ,
.Xr attributes 5